before you get carried away with incorrect assumptions
British Army uniform SDs ( Service Dress) had
5 buttons

canadians also wore SDs as did australians etc etc
The army, especially in the early war moved on horseback, so any soldier who was involved wore spurs ( an infantry regiment for example had approx 80 horses),
he is holding a whip, which makes me think he would be driving a team of horses
i can't make out the badge, a high resolution scan of his cap might show more details but i suspect that is an Army Service Corps ( ASC) badge
chris